Because of the production methods for hot-rolled, slender rolling stock, such as wire rod or bar steel, inherent dimensional defects and other defective locations occur, particularly in the leading ends or lagging ends of the rolling stock. Accordingly, it is necessary to remove the defective end pieces between the parts of the rolling mill train or for the subsequent cold working of the rolling stock. In the production of a wire rod, the defective end pieces must be cut off before the finishing roll group and before the wire rod is wound on a winding drum since it is difficult and time-consuming to shear off or detach the end piece after the wire is wound onto the drum.
Rolling mills for the production of wire rod contain highly developed system components for the economy and production capacity of the overall installation. One of the prerequisites for this is a high rolling speed. The rolling speed in the wire finishing train, in the so-called Morgan finishing group, is more than 100 m per second. When utilizing reserves, the rolling speed can amount to 120 m per second. Thus, the cropping and cutting shears, used in the rolling mill train, must be capable of cropping the rolling stock at high rolling speeds at the leading end or at the lagging end or by cutting it off for sampling or also carrying out emergency cuts during disturbances. Various shear constructions are known for this purpose.
The European Patent Application 0 256 371 Al describes starting and continuous drum shears for high wire speeds. The drum shear for cropping rod wire is designed in such a way that it is swivelable around a vertical axis situated in the blade area and in such a way that a switch arranged upstream is adjustable for the guidance of the rod wire in synchronized transverse movement within two limiting swivel positions in which the rod wire runs outside the cut area of the shears. In this way, the blade drums can carry out several revolutions prior to the cut in order to reach the required high circumferential speeds. However, the blade drums can also rotate in continuous operation. As a result of the swiveling of the switch, e.g. the front end of a rod wire passes through the cut area of the shears so that a front cropping arrives in a deflecting channel leading to the chopper shears. The following rod wire is guided in the channel to the finishing stand or to the coiler by the continued transverse movement of the switch. The synchronized actuating drive for the swiveling of the switch comprises a crank drive combined with a cam drive, by means of which the switch can be switched smoothly and without excessive acceleration for the cut. This shear enables the cropping of the rod wire at determined points and at a determined time with high accuracy and at high rolling speeds.
Rotating cropping and sampling shears for wire rod mill trains is known from the European Patent Application 0 259 600 Al and comprises two blade pairs arranged so as to be offset in the circumferential direction, wherein the blades with radially extending cutting edges are inserted in opposite, approximately planar blade supports supported at a uniform height below the rolling axis. The severing cuts are effected by axial displacement of a blade support in that the latter is inclined at an acute angle of a few degrees relative to the other blade support. Because of the inclined cutting position of the rotating blade, a front cropping with adjoining sample piece or a sample piece alone or a back cropping with following sample piece can be ejected laterally into a sample channel. Thus, it is possible with these shears to cut out sample pieces at desired locations of a rapidly running rolling stock and to select a continuous operation of the shears.